Abstract
A novel analytical method is introduced that measures the volume fraction of paraffins, olefins, naphthenes, and aromatics (PONA) in hydrocarbon liquids having distillation endpoints (American Society for Testing and Materials, ASTM D 2887) of at least 300°C. The method uses on-line column switching high-performance liquid chromatography (HPLC) with dielectric constant detection (DCD), i.e., HPLC-DCD. A specially configured hydrocarbon group-type analyzer system is used. The PONA separations are achieved using an olefin-selective column, an unsaturate-selective column, three naphthene-selective columns, two six-port switching valves, and Envron 123 as the mobile phase. The HPLC-DCD system ensures a genuine uniformity of response (less than 2.5% relative standard deviation) independent of the carbon number distribution of the sample or the group type. Unity response factors are sufficient for accurate quantitation. On the basis of complex solutions of hydrocarbon standards, the accuracy for each structural group type is within 2% absolute. The chromatographic limit of detection of the present system for naphthenes is less than 4.0 vol.% ( ca. 40 μg), for a kerosene fuel containing a wide carbon number distribution of both mono- and di-cycloparaffins, and is approximately 1.0 vol.% ( ca. 10 μg) for olefins. Sample turnaround time is approximately one hour. The results of the PONA analysis scheme are compared to those of the standard fluorescent indicator adsorption (FIA) liquid displacement method (ASTM D 1319), an alternative to the FIA method developed in this laboratory using HPLC-DCD, and a mass spectrometric method (ASTM D 2789) on standard mixtures and real-world products. For determining total naphthenes and olefins in the gasolines and kerosenes selected for study, the HPLC-DCD system was superior.
Published Version
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